The present invention relates to compositions which are used to control sulfur oxide (SOx) emissions from fluid catalytic cracking (FCC) operations, and more particularly to SOx gettering compositions that are capable of capturing SOx during the oxidative regeneration of FCC catalysts, and releasing sulfur as H.sub.2 S in the reducing atmosphere of the catalytic cracking reaction zone.
Compositions which have been used to control SOx emissions typically comprise magnesia, alumina and rare earth oxides.
In particular, U.S. Pat. No. 4,472,267, U.S. Pat. No. 4,495,304 and U.S. Pat. No. 4,495,305 disclose SOx control compositions which contain magnesia-alumina spinel supports in combination with rare-earths such as ceria and lanthana, and U.S. Pat. No. 4,836,993 discloses the preparation of magnesium aluminate (MgAl.sub.2 O.sub.4) and magnesia-alumina composites that are combined with a rare earth and used as sulfur oxide absorbent in FCC processes.
While prior compositions have been successfully used to control the SOx emissions from FCC units, the industry requires compositions that are efficient for both the pick-up of SOx in the catalyst composition during regeneration, and the release as H.sub.2 S in the cracking reaction.
In addition, SOx control agents which are used in the form of separate particulate additives must have hardness and attrition properties that enable the additive to remain in a circulating FCC catalyst inventory.